Method and arrangement for improved controllability of fuel cell stacks

Abstract

Exemplary systems and methods for adjusting current values in a fuel cell system for producing electricity with fuel cells, include drawing major part of the current from at least one serial connection. An adjusting circuit adjusts current values by drawing or supplying current of at least one stack of individual fuel cell stacks or current of at least one group of the groups of stacks within the serial connection. The adjusting circuit is integrated with the at least one stack of individual fuel cell stacks or with the at least one group of the groups of stacks. Compensation current of the at least one stack or group is a small percentage of a major part of the current in the serial connection of stacks.

What is claimed is: 
     
       1. An arrangement for adjusting current values of fuel cells in a fuel cell system for producing electricity with fuel cells, wherein each fuel cell in the fuel cell system includes an anode side, a cathode side, an electrolyte between the anode side and the cathode side, wherein the fuel cell system includes at least two electrically serial connected individual fuel cell stacks or groups of stacks, each stack having at least one fuel cell, the arrangement for adjusting current values in the fuel cell system comprising:
 cabling for drawing a first current from the serial connection wherein the first current will be a major part of current of said serial connection; 
 at least one adjusting circuit for adjusting the current of said serial connection by drawing or supplying a negative or positive compensation current from the fuel cell stacks or groups of stacks within the serial connection; and 
 a cabling connection for integrating the at least one adjusting circuit with the fuel cell stacks or groups of stacks within the serial connection for arranging said compensation current, the compensation current being in a magnitude scale of 0-10% compared to values of the first current, to pass via the at least one adjusting circuit, the current of said serial connection in the at least two individual fuel cell stacks or groups of stacks being a sum of the first current and the compensation current, 
 wherein the at least one adjusting circuit includes switch converter circuitry for controlling the compensation current in the at least two individual fuel cell stacks or groups of stacks. 
 
     
     
       2. The arrangement in accordance with  claim 1 , wherein said compensation current is 0-3% compared to the first current in said serial connection of stacks. 
     
     
       3. The arrangement in accordance with  claim 1 , wherein said cabling connection for integrating the at least one adjusting circuit includes circuitry for measuring voltage of the at least two fuel cell stacks or groups of stacks by using common cables for the at least one adjusting circuit and at least one common circuit board. 
     
     
       4. The arrangement in accordance with  claim 1 , wherein the at least one adjusting circuit is an isolated high-frequency transformer arrangement. 
     
     
       5. The arrangement in accordance with  claim 1 , wherein the at least one adjusting circuit is a non-isolated cascaded converter arrangement including the switch converter circuitry for producing control signals, switches to be controlled to open and closed positions and wherein the switch converter circuitry controls the compensation current by utilizing said control signals in controlling the switches to open or closed positions to individually adjust the current of each fuel cell stack or group of stacks. 
     
     
       6. A method for adjusting current values of fuel cells in a fuel cell system for producing electricity with individual fuel cell stacks or groups of stacks, comprising:
 drawing a first current from at least one serial connection of the individual fuel cell stacks or groups of stacks, wherein the first current will be a major part of current of said serial connection; 
 adjusting the current of said serial connection by drawing or supplying a positive or negative compensation current to or from at least one stack of said individual fuel cell stacks or at least one group of said groups of stacks within the serial connection having other individual fuel cell stacks or other groups of stacks, and by integrating at least one adjusting circuit with the at least one stack of individual fuel cell stacks or with the at least one group of groups of stacks for arranging said compensation current of said at least one individual stack or of said at least one group, the compensation current being in a magnitude scale of 0-10% compared to values of the first current, to pass via the at least one adjusting circuit, wherein the current of said serial connection in the at least one individual fuel cell stack or in the at least one group of stacks being said major part of the first current and is summed with the compensation current; and 
 controlling the compensation current in the at least one individual fuel cell stack or in the at least one group of stacks by utilizing the at least one integrated adjusting circuit. 
 
     
     
       7. The method in accordance with  claim 6 , wherein said compensation current is 0-3% of the first current in said serial connection of stacks. 
     
     
       8. The method in accordance with  claim 6 , wherein said at least one adjusting circuit is integrated with circuitry for measuring voltage of fuel cell stacks by using common cables for said at least one adjusting circuit and at least one common circuit board as said circuitry for measuring voltage use. 
     
     
       9. The method in accordance with  claim 6 , wherein the at least one adjusting circuit is an isolated high-frequency transformer arrangement. 
     
     
       10. The method in accordance with  claim 6 , wherein control signals are produced and switches are controlled by utilizing switch converter circuitry to open and close positions on the basis of said control signals to individually adjust the current of each fuel cell stack. 
     
     
       11. A system for adjusting current values of fuel cells in a fuel cell system for producing electricity with fuel cells, wherein each fuel cell in the fuel cell system includes an anode side, a cathode side, an electrolyte between the anode side and the cathode side, wherein the fuel cell system includes at least two electrically serial connected individual fuel cell stacks or groups of stacks, each stack having at least one fuel cell, the system for adjusting current values in the fuel cell system comprising:
 cabling for drawing part of a first current from the at least one serial connection wherein the first current will be a major part of current of said serial connection; 
 at least one adjusting circuit for adjusting the current of said serial connection by drawing or supplying a positive or negative compensation current from at least one stack of said individual fuel cell stacks or of at least one group of said groups of stacks within the serial connection; and 
 a cabling connection for integrating the at least one adjusting circuit with the at least one stack of individual fuel cell stacks or with the at least one group of groups of stacks for arranging said compensation current of said at least one stack or of said at least one group, the compensation current values being 0-3% of a magnitude of the first current in at least said serial connection of stacks, wherein to pass via the at least one adjusting circuit, the current of said serial connection in the at least one individual fuel cell stack or in the at least one group of stacks being a sum of the first current and the compensation current, 
 wherein the at least one adjusting circuit includes switch converter circuitry for controlling the compensation current in the at least one individual fuel cell stack or in the at least one group of stacks.